Volume 8, Issue 4 - April 2007
All Together Now
Seeing clearly was a cause of concern for members of the Insulating Glass Manufacturers Alliance (IGMA) in February. During its annual meeting, held February 21-24 in Tampa, Fla., IGMA’s visual quality working group (VQWG) worked to clear up its guidelines on visual obstructions in insulating glass units (IGUs). VQWG members discussed the guideline’s requirement that certain obstructions should not be allowed was excessive as dirt, debris and fingerprints can’t be absolutely eliminated in IGUs. Other members were concerned that visual obstructions addressed by the IGMA guideline might already be addressed in other industry documents, notably, ASTM C1036 Standard Specification for Flat Glass.
“The homeowner’s not going to care what [type] it is, it’s an obstruction,” said Jeff Haberer of Cardinal Glass Industries, of the comment that there’s no way to tell what the obstruction is unless the unit is pulled apart.
I Can See Clearly Now the Dirt and Debris Are Gone
The document also states that the marks on flat glass used in the IGU should comply with ASTM C1036 and that sightline infringement shall be no greater than 1⁄8 inch along any sightline of the IGU.
“When you put out a document that says ‘not allowed’ … my concern is that we’re going to be rejecting product that’s perfectly sellable,” said Haberer. “We’re mandating perfection, and I think we need to scale it back here.”
Haberer wasn’t alone.
“In order to be practical, you have to allow certain imperfections,” said Bill Hammon of Associated Laboratories Inc. “Minimizing is the key word.”
Following discussion about what constitutes a visual obstruction, the group agreed that many of the items listed in section four should, in fact, be quantified. The group agreed only two items, fogging and suction/vacuum cup marks, should continue to be listed as “not allowed” in the document.
Several group members commented that the type and quality of the lighting could also affect the visibility of an obstruction.
Chris Barry of Pilkington suggested the document state that standard lighting conditions be used to determine the visibility of an obstruction.
Bruce Virnelson of PRC Desoto International reminded the group that fog is sensitive to lighting. “There has got to be some sort of comment in there on lighting,” said Virnelson.
However, others noted that lighting conditions can’t necessarily be controlled in the field.
“If you’re getting very prescriptive with the lighting, how are you going to meet that in the field?” said Tracy Rogers of Edgetech.
With these new questions in mind, the working group will take another look at this section before the summer meeting.
Getting Their Fill of Gas Content Concerns
“It’s certainly a major step toward putting these two programs together,” said Margaret Webb, IGMA executive director.
A motion to make gas content certification voluntary rather than mandatory was passed. Several committee members said that making gas content certification mandatory adds substantive cost for manufacturers with few gas-fill products that still want to certify the durability of their products. The group accepted the change to voluntary certification, with the caveat that they hope to require mandatory gas content certification again in the future.
“There was real resistance to carrying two types of spacer, labeled and unlabeled,” Webb said. “[IG manufacturers] may choose to participate in just one program.”
The committee members also addressed the question of whether testing double-glazed units would qualify in lieu of testing triple-glazed units. They approved the schedule following IGCC for testing triple-glazed units every four years. Double-glazed units would be tested in interim years.
Addressing Distortion of Vinyl Siding
“Glass does reflect and it does shine on other buildings and if those buildings are of susceptible materials there could be problems,” Haberer said.
Vinyl is particularly susceptible to bending and cracking from heat.
“Other siding products are not as vulnerable as vinyl,” he said. “It’s due to the relatively low distortion temperature of vinyl.”
The distortion of vinyl begins to occur at temperatures of 160º-165º Fahrenheit. Dark colors of siding can have up to 80 percent absorption of the sun’s rays and Haberer noted that some building construction can increase the amount of heat hitting the building. He showed images of inside corners with windows, where the rays hit the siding directly at the same time that rays deflected from the window hit the perpendicular wall as well, further raising the temperature of the vinyl.
The study examined the impact of reflective coatings on this type of damage.
“The more reflective coatings out there today that are getting more popular, are going to create this problem,” he said.
While reflective glass created problems, researchers found that even clear glass can become a significant heat source.
“The study indicates that even clear glass can raise siding above distortion temperature,” Haberer said.
He recommended following the advice of the Vinyl Siding Institute (VSI) at this point, since no solution is currently available from the glass industry. VSI recommended installing a screen in the problem-causing window or installing an awning over the window to break the line of light reflection. The institute also suggests the use of shrubbery to protect the impacted area of siding from reflections or radiation.
Testing for Energy Consumption
In Barry’s test, the two houses were benchmarked by using a high solar transmission low-E coating on surface 3 of all of the double-glazed argon-filled windows and patio doors. Twenty-three windows and both the fixed and sliding portions of a patio door were included. Next, Barry explained, the IGUs in the test house were replaced by insulating glazing systems with a low solar transmission low-E coating on surface 2 of the double-glazed argon-filled windows.
The house was tested for four weeks during the winter, January 19-February 15, 2006, when the average temperature measured 24.4º Fahrenheit. Natural gas and electricity consumption and air and window surface temperature measurements were recorded. Preliminary results showed that the use of low solar transmission glazing systems increased the gas consumption in the test house by about 8.7 percent relative to its performance with the high solar transmission glazing. The electric consumption was increased by about 1.3 percent as a result of the reduced solar heat gain.
Barry said the initial results suggest energy savings using high SHGC and low-E glazing, from New York to Seattle and further north. He added that detailed results of the study, including the results of monitoring the windows during the hot and humid summer months, will be presented at a future IGMA meeting.
The Effects of Hurricanes on IGU Performance
Lingnell answered his own question by giving examples of historic hurricanes and outlining the science of how hurricanes are created. He explained that the lower the atmospheric pressure, the worse the storm. That led into a discussion on preparing IGUs for being under pressure in a hurricane.
“The pressures that occur during the hurricanes are low pressure and they are usually substantially lower than the pressure that exists in the sealed IGU,” said Lingnell. “The changes in barometric pressure will cause stress on the edge seals and stresses in the glass.” Glass is elastic and is going to move under pressure, and that movement should be accounted for in both the glass and the surrounding components, according to Lingnell.
“Hurricane speeds can relate to a substantial pressure on the glass and, as such, the supporting members should be reviewed closely to find out how much deflection will be predicted during the loading conditions,” he said.
In particular, Lingnell explained that high deflection can cause shear stress on the bond of the IG sealants. He said it needs to be verified that the stress on the edge seal is not in a zone that is detrimental to the sealant.
Water intrusion is another hurricane-related problem. Part of the problem, Lingnell said, is that when water is driven into the unit by hurricane-force winds, it can’t necessarily find a way out.
“The glazing condition must be designed so that water and moisture have a way of exiting so as not to be detrimental to the sealants,” he said.
Lingnell noted that water trapped in IGUs can be a major culprit of seal failures.
“Look for let-go or bond-loss conditions that lead to seal failures and loss of seal integrity due to water entrapment in the glazing system,” Lingnell said. “This one’s kind of important.”
Lingnell said that he would like to see more consideration for keeping water out of IGUs.
Finally, he addressed a common question he hears asked of IGMA: “Does a hurricane cause a seal failure?”
It depends on the unit and should be observed on a case-by-case basis, he said. A number of factors could contribute to seal failure and some of these are the result of a hurricane.
IGMA’s next meeting will be held June 11-13, 2007, at the Hyatt Regency Huntington Beach Resort and Spa in Huntington Beach, Calif.
Megan Headley is a contributing writer for DWM Magazine.